Transmissions for motor vehicles are designed, among others, as so-termed dual clutch transmissions in which in each case an input shaft is associated with a sub-transmission and in which the input shafts of the two sub-transmissions can be connected by a respectively associated powershift element with a drive input such as a combustion engine or an electric motor, the two powershift elements then being combined in the form of a dual clutch. The gears that can be produced by means of such a transmission are then divided in alternation between the two sub-transmissions, so that for example one sub-transmission produces the odd-numbered gears and the corresponding other sub-transmission produces the even-numbered gears. It is also known to produce the individual gear steps by means of one or more gearwheel stages or planes, each with a different gear ratio step. By virtue of corresponding shifting elements these can be connected into the force or torque flow between the drive input and the drive output, so that a corresponding desired transmission ratio is produced in each case between the drive input and the drive output.
Thanks to the alternate division of the gears between the two sub-transmissions it is possible, while driving in a gear associated with one of the sub-transmissions, already to preselect a subsequent gear in the respective other sub-transmission by appropriate actuation of the shifting devices, so that an ultimate shift to the subsequent gear is enabled by opening the powershift element of the one sub-transmission and, shortly thereafter, closing the powershift element of the other sub-transmission. In this way the gears or gear steps of the transmission can be shifted under load, which improves both the ability of the motor vehicle to accelerate and the comfort of gearshift processes for the vehicle's driver, since the gearshift takes place essentially without traction force interruption.
Such dual clutch transmissions can also be made with an intermediate countershaft arrangement in addition to the drive input and the drive output, so that a more compact structure is produced in the axial direction. Furthermore, it has also become known to provide dual clutch transmissions with a range group on the output side so as to increase the number of gears that can be obtained by means of the transmission.
From DE 10 2006 054 281 A1 a transmission for a motor vehicle in the form of a dual clutch transmission has become known. In this case the dual clutch transmission comprises two sub-transmissions, each with an input shaft. By connecting the input shafts by way of a respective powershift element, the two sub-transmissions can each be connected in alternation into a force or torque flow from a drive input to a drive output, wherein the input shaft of the first sub-transmission is in the form of a central transmission shaft and the input shaft of the second sub-transmission is in the form of a hollow transmission shaft. Furthermore an output shaft is provided which is designed as the drive output of both the sub-transmissions, so that rotational movement of the drive input can be transmitted to the drive output by way of a plurality of gear ratio steps in which the force and torque flow is led through a countershaft arrangement. During this at least two wheel planes are connected into the force and torque flow by actuating associated shifting elements, so that by a combination of the actuation of the shifting elements and the force and torque flow via corresponding wheel planes, several gear steps can be obtained. Likewise, a straight-through transmission of the rotational movement of the drive input to an output shaft of the drive output is possible by actuating appropriate shifting elements.